Study On Carrier Synchronization Of Weak Sequence Spread Spectrum Signal

As the development of low-orbit satellites and near space hypersonic aircraft inTT&C(short for telemetry, track and command)communication, there is large Dopplerfrequency shift, if not removed, the receiver may not work, how to realize carriersynchronization under this high dynamic environment is a key issue. The BPSK directsequence spread spectrum system is widely used in TT&C communication, therefore thestudy on the carrier synchronization of BPSK direct sequence spread spectrum signal issignificant.Based on the problem that the traditional phase lock loop cannot track the processof the Doppler frequency shift and initial Doppler frequency exceed the locking scope,frequency estimation technologies such as the FFT-based technology and cyclicspectrum estimation technology are introduced. Using the Hilbert complex vector FFTtechnology can distinguish between positive and negative frequency offset. For the highdynamic problem, Delay related FFT and matched Fourier transform method canestimate the rate of change of frequency. For low SNR, the time diversity method isstudied. The paper also discusses the structure of the phase locked loop and frequencylocked loop and how to design them. And also deeply analysis and simulate the impactof various parameters on the PLL and FLL.The conclusion that through estimating thefrequency deviation rate to decrease the dynamic of the signal the same trackingaccuracy can be accessed under lower signal-to-noise ratio is reached.Finally, the carrier synchronization is realized under high dynamic environmentwith Doppler frequency offset as much as1MHz and frequency offset deviation rate asmuch as200KHz per second. The simulation of BPSK spread spectrum communicationsystem including code and carrier synchronization with SNR at-8dB is executed. Undersuch dynamic environment, two stages of frequency estimation and dynamic correctionplus FLL and PLL tracking are used to achieve the tracking accuracy less than10Hzfrom the original100Hz. Through signal extraction and accumulation the frequencyoffset and frequency offset deviation rate can be effectively estimated using MatchedFourier Transformation method at the signal-to-noise ratio of-35dB.